DESCRIPTION (provided by investigator): An estimated 192,200 women were diagnosed with breast cancer in 2001, more than half of whom were 60 years of age or older. Of concern is that while breast cancer-specific mortality rates have declined among women less than 70 years old, they are either stable (70-79 year olds) or are increasing (80+ year olds) among those 70 years or older. One explanation for this is that older women receive less than standard therapy more frequently than younger women. Neither efficacy nor effectiveness data to date justify this pattern of care. Taking advantage of the Health Maintenance Organization (HMO) Cancer Research Network, we propose to conduct a historical cohort study of an unselected group of older women (>65 years of age) newly diagnosed with early stage breast cancer (stages I-II) between 1990 and 1994. Specifically, we will (1) Compare the effectiveness of standard primary tumor therapy (breast conserving surgery, axillary dissection, and radiation therapy or modified radical mastectomy) versus other than standard therapy in preventing breast cancer recurrences and mortality, adjusting for co-morbidity, tumor characteristics, geographic site, and demographic characteristics; (2) Determine the extent to which the addition of systemic adjuvant therapy (chemotherapy, hormonal therapy, or the combination of chemotherapy and hormonal therapy) modifies the effectiveness of standard and other than standard primary tumor therapy in preventing breast cancer recurrences and mortality; (3) Describe patterns of surveillance testing for breast cancer recurrence and determine the extent to which surveillance testing is associated with a reduction in breast cancer-specific mortality; and (4) Identify provider, tumor, and patient characteristics associated with the receipt of standard primary tumor therapy and systemic adjuvant therapy in older women with newly diagnosed early stage disease in the HMO setting. Six sites from throughout the United States will together identify and follow 2180 women for ten years. Both electronic and medical record data sources will be used to collect information that will allow us to characterize the separate and joint effects of treatment, tumor, and patient characteristics on breast cancer recurrence and mortality. Findings from this study will inform clinical practice, particularly the care of older women with co-morbidities who are unlikely to participate in clinical trials.